1. Field of the Invention
This invention relates to vibrating beam or tuning fork force transducers and, more particularly, to a system for isolating the mounting pads for the beam or tuning fork from longitudinal vibrations of the beam or tuning fork induced by transverse vibrations of the beam or tuning fork.
2. Description of the Prior Art
Conventional flexurally vibrating force transducers are highly accurate and completely satisfactory in many applications. However, optimum performance from these transducers is limited by the coupling of energy from the vibratory element--either a beam or the tines of a tuning fork--to the mounting pads which support the element. This energy loss lowers the "Q" (quality factor which is proportional to the ratio of the energy stored to the energy lost each cycle) of the device so that the frequency of vibration of the vibratory element does not precisely respond to changes in the axial force applied to the vibratory element. In the extreme, this energy loss can be so large as to effectively preclude vibration at certain frequencies resulting in marked discontinuities of frequency with axial force applied to the transducer element.
An elongated vibratory element couples energy to the mounting pads in two distinctly different modes. First, transverse movement of the element produces rotational moments about a rotational axis extending through the mounting pad perpendicularly to the plane of beam vibration. This problem has been largely solved by the technique disclosed in U.S. Pat. No. 3,470,400 issued to Weisbord. As the vibratory element moves transversely, however, it also imparts forces to the mounting pads toward and away from each other since the effective length of the vibratory element varies.
While isolating the mounting pads from one type of vibratory transmission has greatly improved the performance of conventional digital force transducers, the energy coupled to the mounting pads through the other type of vibratory transmission can still result in significant performance degradation.